The present invention relates to a method for recovering various kinds of amino acids from a mixed solution comprising inorganic acid salts, coloring matters, ashes, betaines, amino acids and non-electrolytes such as saccharides. In the course of producing sucrose from sugar beets, impurities other than sucrose move into molasses. The molasses still contains sucrose in about a half amount, so that sucrose has further been recovered from the molasses by ion chromatography (hereinafter also referred to as xe2x80x9cCRxe2x80x9d). Residues containing sucrose which can not be recovered and trace amounts of amino acids have been treated as xe2x80x9cCR waste liquorxe2x80x9d. Further, in the production of sucrose, when ion exchange resins used for purification of sugar liquid in the process of sugar manufacture are regenerated, trace amounts of amino acids adsorbed by the ion exchange resins are eliminated together with regenerating solutions to flow out. This effluent liquor has also been treated as xe2x80x9cresin waste liquorxe2x80x9d. These CR waste liquor and resin waste liquor have hitherto been subjected to the activated sludge process and discarded, or only condensed for utilization as organic fertilizer. The present invention relates to a novel method for recovering amino acids, which makes it possible to recover trace amounts of amino acids existing in such waste liquor.
Previously, CR has been utilized as one method for separating respective ingredients from solutions containing the multiple ingredients, such as natural material solutions. However, it has been practically impossible to industrially utilize CR as such for separating trace amounts of ingredients, considering the price of products obtained. Because it necessitates large-scale equipment and a large amount of treating liquid. Many processes have been therefore contrived for industrially using CR. For example, the present inventors have disclosed in Japanese Patent Publication No. 56-39640 that only fractions having sucrose/raffinose ratios within a specific range are collected by separation through a salt type strongly acidic ion exchange resin, and fractionally crystallized, which makes it possible to industrially produce raffinose from sugar beet molasses. Further, as to a method for separating materials similar to those in the present invention, one invention is disclosed in Japanese Patent Laid-Open Publication (Hei) 6-276995. This invention is directed to a method for producing a raw flavoring material, which comprises supplying CR waste liquor or resin waste liquor to a sodium type strongly acidic ion exchange resin to allow amino acids to be adsorbed thereby, and then, eluting them with a solution of sodium hydroxide through a hydrogen ion type weakly acidic ion exchange resin connected to the back of the sodium type strongly acidic ion exchange resin.
The object of the invention described in Japanese Patent Laid-Open Publication (Hei) 6-276995 is to obtain an amino acid-rich fraction, and the fraction can be used as a raw flavoring material. However, the fraction contains materials other than amino acids, and this invention is not directed to a method for recovering only amino acids.
An object of the present invention is to provide a method for recovering various kinds of amino acids from a solution containing trace amounts of amino acids in a highly concentrated inorganic acid salt or a highly concentrated non-electrolyte such as saccharide, for example, CR waste liquor or resin waste liquor.
The present invention relates to a method for recovering amino acids, which comprises (1) supplying a mixed solution containing inorganic acid salts, coloring matters, ashes, betaines, amino acids and non-electrolytes such as saccharides to a first-step first resin layer comprising a sodium type strongly acidic ion exchange resin (hereinafter also referred to as an xe2x80x9cNa type IERxe2x80x9d) or a potassium type strongly acidic ion exchange resin (hereinafter also referred to as a xe2x80x9cK type IERxe2x80x9d), (2) separating an effluent which flows out of the first resin layer using water or an aqueous solution of a caustic alkali as an eluent into at least a first fraction containing coloring matters, acidic amino acids and ashes, a second fraction containing neutral amino acids and saccharides, and a third fraction containing betaines, (3) supplying the second fraction to a second-step resin layer comprising at least one resin selected from the group consisting of an ammonium type strongly acidic ion exchange resin (hereinafter also referred to as an xe2x80x9cNH4 type IERxe2x80x9d), a calcium type strongly acidic ion exchange resin (hereinafter also referred to as a Ca type IERxe2x80x9d) and a magnesium type strongly acidic ion exchange resin (hereinafter also referred to as an Mg type IERxe2x80x9d), and (4) recovering various kinds of amino acids contained in an effluent which flows out of the second-step resin layer.
In the present invention, the term xe2x80x9cneutral amino acidsxe2x80x9d means neutral amino acids including neutral aromatic amino acids such as tyrosine, in a broad sense.
Also, in the present invention, the term xe2x80x9ca caustic alkalixe2x80x9d means alkali hydroxide including sodium hydroxide and potassium hydroxide.
As to an eluent used for the ion exchange resin in the present invention, an aqueous solution of ammonia is used for the NH4 type IER, water or an aqueous solution of a caustic alkali for the Na type or K type IER, and water for the Ca type IER and the Mg type IER.
Further, when the above-mentioned second-step resin layer is the Ca type IER, the effluent which flows out of the second-step resin layer may be further partly supplied to a third-step resin layer comprising the Mg type IER to recover various kinds of amino acids contained in an effluent which flows out of the third-step resin layer using water as an eluent (which means xe2x80x9crecovering method 2-2-Axe2x80x9d described later).
Furthermore, when the above-mentioned second-step resin layer is the Mg type IER, the effluent which flows out of the second-step resin layer may be further partially supplied to a third-step resin layer comprising the Ca type IER to recover various kinds of amino acids contained in an effluent which flows out of the third-step resin layer using water as an eluent (which means xe2x80x9crecovering method 3-2-Axe2x80x9d described later).
As the eluent for the above-mentioned first resin layer, there may be used an aqueous solution of a caustic alkali having a pH of 8.5 to 11.0.